The present invention is related to a method and apparatus for transferring heat between a fluid and a material onto which the fluid is impinged. More specifically, the present invention is related to an impinging jet nozzle that can improve the efficiency of heat transfer between the fluid passing through the nozzle and the material onto which the fluid is impinged.
Impingement of fluids, such as air or other gasses or liquids, onto a surface has been recognized and used for years in many situations, especially manufacturing, as a method for providing and/or alter the properties of products such as webs. In particular, impingement has been used during the manufacture of fibrous structures, such as paper webs. Typically, during the manufacture of paper, large amounts of water must be removed from the web that is created before it can be converted into an end product or used by the consumer. Some of the most commonly used papermaking techniques form an initial paper web from an aqueous dispersion of fibers containing more than 99% water and less than 1% papermaking fibers. Generally, almost 99% of this water is removed mechanically, yielding a fiber-consistency of about 20%. Then, pressing and/or thermal operations, and/or through-air-drying, or any combination thereof, typically remove some of the remaining water, increasing the fiber-consistency of the web to about 60%. In the final drying operation (typically using a drying cylinder and impinging jets) the web is dried such that the fiber-consistency of the web is about 95%.
Because such a great amount of water needs to be removed, water removal is one of the most energy-intensive operations in industrial papermaking processes. Further, within the water removal operations, thermal energy is one of the most costly and inefficiently used resources. Therefore, more efficient methods of water removal, and especially more efficient thermal operations, may provide significant benefits for the papermaking industry, such as increased machine capacity and reduced operational costs.
As can be seen in U.S. Pat. Nos. 3,577,651; 3,739,490; 3,771,239; 3,895,449; 3,936,953 and 4,274,210, the need to improve efficiency of heat transfer has been generally identified in the prior art and many attempts have been made to solve the problem. However, there is still a need for more efficient, less complex systems that perform effectively at very high rates of speed, especially when the end product, like paper, is disposable.
Accordingly, it would be desirable to provide a method and/or apparatus for more efficiently transferring heat from a fluid to a moving material. Further, it would be desirable to provide an improved nozzle to be used in an impingement operation. Even further, it would be desirable to provide an asymmetric nozzle through which air or gas may be impinged onto a surface to more efficiently transfer heat from the air or gas to the surface upon which the air or gas is impinged. It would also be desirable to provide an improved process and apparatus for drying webs, such as paper webs.
The present invention provides an efficient method and apparatus for exchanging heat between a fluid and a material onto which the fluid is impinged. One embodiment of the apparatus includes: a support element designed to receive a material thereon and to carry the material in a machine direction, the material having a surface oriented away from the support element; at least one fluid supply designed to produce and discharge a fluid; at least one nozzle having an open area formed by an upstream wall and a downstream wall relative to the machine direction, the nozzle connected to the fluid supply and disposed generally adjacent to the support element and spaced apart therefrom so as to form an impingement distance between each wall of the nozzle and a plane generally corresponding to the surface of the material, wherein the impingement distance between the upstream wall and the plane is greater than the impingement distance between the downstream wall and the plane such that at least a portion of the fluid is delivered through the nozzle to a predetermined portion of the material carried by the support element in a direction that is counter to the machine direction; an upstream collection device which is disposed upstream relative to the nozzle; and a downstream collection device which is disposed downstream relative to the nozzle.
One embodiment of the method of the present invention includes the steps of: providing at least one nozzle having an opening formed by an upstream wall and a downstream wall relative to the machine direction, the nozzle connected to a fluid supply and disposed generally adjacent to the support element and spaced apart therefrom so as to form an impingement distance between each wall of the nozzle and a plane generally corresponding to a surface of a material onto which the fluid is to be impinged, wherein the impingement distance between the upstream wall and the plane is greater than the impingement distance between the downstream wall and the plane; providing a material adjacent the opening in the nozzle, the material moving in the machine direction; and supplying a fluid from the fluid supply through the nozzle onto the material such that at least a portion of the fluid is delivered in a direction that is counter to the machine direction.